Copper substrate for deposition of graphene

ABSTRACT

Technologies are presented for growing graphene by chemical vapor deposition (CVD) on a high purity copper surface. The surface may be prepared by deposition of a high purity copper layer on a lower purity copper substrate using deposition processes such as sputtering, evaporation, electroplating, or CVD. The deposition of the high purity copper layer may be followed by a thermal treatment to facilitate grain growth. Use of the high purity copper layer in combination with the lower purity copper substrate may provide thermal expansion matching, compatibility with copper etch removal, or reduction of contamination, producing fewer graphene defects compared to direct deposition on a lower purity substrate at substantially less expense than deposition approaches using a high purity copper foil substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional under 35 U.S.C. §121 of and claimspriority under 35 U.S.C. §120 to U.S. patent application Ser. No.13/817,533 filed on Feb. 18, 2013, which is the National Stage filingunder 35 U.S.C. §371 of PCT Application Ser. No. PCT/US12/39633 filedMay 25, 2012. The disclosures of the U.S. patent application and the PCTApplication are hereby incorporated by reference in their entireties.

BACKGROUND

Unless otherwise indicated herein, the materials described in thissection are not prior art to the claims in this application and are notadmitted to be prior art by inclusion in this section.

Graphene monolayers are one-atom-thick planar sheets of sp2-bondedcarbon atoms with unique physical properties. This material is ofinterest for high speed integrated circuits, flexible displays, solarcells, and many other scientific and technological applications.However, many such applications may be dependent on graphene with a lowdefect density. One approach for producing large films of single layergraphene is chemical vapor deposition (CVD) on copper substrates. It hasbeen demonstrated that CVD graphene grown on a 99.8% pure coppersubstrate may produce more than ten times the number of defects comparedto CVD graphene grown on a 99.999% pure copper substrate. Unfortunately99.999% pure copper may cost approximately ten to one hundred times thatof 99.8% copper. Since the copper is etched away in the fabricationprocess, the value of the purity may be lost even though the copper maybe reclaimed.

The present disclosure appreciates that improving the quality of CVDgraphene may be a complex undertaking.

SUMMARY

The following summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects, embodiments,and features described above, further aspects, embodiments, and featureswill become apparent by reference to the drawings and the followingdetailed description.

The present disclosure generally describes methods, apparatus, andcomputer program products for to improving the growth of graphene bychemical vapor deposition.

According to some examples, a method of manufacturing graphene isprovided. The method may include providing a copper substrate that mayinclude a first copper layer in contact with a second copper layer. Thefirst copper layer may be characterized by a first copper percentage byweight and the second copper layer may be characterized by a secondcopper percentage by weight. The second copper percentage may be greaterthan the first copper percentage. The method may also include growing agraphene monolayer via chemical vapor deposition on the second copperlayer.

According to some examples, a copper substrate for growing a graphenemonolayer is provided. The copper substrate may include a first copperlayer characterized by: a first copper percentage by weight, a firstoxygen percentage by weight, and a first thickness. The copper substratemay also include a second copper layer in contact with the first copperlayer. The second copper layer may be characterized by: a second copperpercentage by weight, a second oxygen percentage by weight, and a secondthickness. In the copper substrate, the second copper percentage may begreater than the first copper percentage: the second oxygen percentagemay be about the same or less than the first oxygen percentage; and thesecond average thickness may be less than the first average thickness.

According to some examples, a graphene-copper composite is provided. Thegraphene-copper composite may include a first copper layer characterizedby: a first copper percentage by weight, a first oxygen percentage byweight, and a first thickness. The graphene-copper composite may includea second copper layer having a first surface in contact with the firstcopper layer. The second copper layer may be characterized by: a secondcopper percentage by weight, a second oxygen percentage by weight, and asecond thickness. The graphene-copper composite may also include agraphene monolayer in contact with a second surface of the second copperlayer. In the graphene-copper composite, the second copper percentagemay be greater than the first copper percentage; the second oxygenpercentage may be about the same or less than the first oxygenpercentage; and the second average thickness may be less than the firstaverage thickness.

According to some examples, a system for manufacturing a coppersubstrate for growing graphene is provided. The system may include adeposition chamber; a sample stage configured to hold a copper substratein the deposition chamber; a copper deposition source; a cleaning agentsource configured to direct cleaning agent to the copper substrate heldby the sample stage; a sensor configured to determine a thickness of alayer deposited by the copper deposition source; a heater configured toheat the copper substrate held by the sample stage to an annealingtemperature of about 750° C. to about 1000° C.; a gas source configuredto provide a thermal annealing gas to the copper substrate held by thesample stage; and a microprocessor. The microprocessor may be coupled tothe deposition chamber, the sample stage, the copper deposition source,the cleaning agent source, the sensor, and the heater. Themicroprocessor may be programmable to: employ the sample stage to hold afirst copper layer in the deposition chamber; employ the cleaning agentsource to direct cleaning agent to the first copper layer, employ thecopper deposition source and the sensor to deposit a second copper layeron the first copper layer, wherein the second copper layer may bethinner compared to the first copper layer; and employ the heater andthe gas source to thermally anneal the first copper layer at the coppersubstrate.

According to some examples, a computer-readable storage medium havinginstructions stored thereon for manufacturing a copper substrate forgrowing graphene is provided. The instructions may include providing afirst copper layer cleaning a surface of the first copper layer,depositing a second copper layer on the cleaned surface of the firstcopper layer to form the copper substrate; and thermally annealing thecopper substrate. The first copper layer may be characterized by: afirst copper percentage by weight, a first oxygen percentage by weight,and a first thickness. The second copper layer may be characterized by:a second copper percentage by weight, a second oxygen percentage byweight, and a second thickness. The second copper layer may be depositedsuch that one or more of: the second copper percentage may be greaterthan the first copper percentage, the second oxygen percentage may beabout the same or less than the first oxygen percentage, and/or thesecond average thickness may be less than the first average thickness.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of this disclosure will become morefully apparent from the following description and appended claims, takenin conjunction with the accompanying drawings. Understanding that thesedrawings depict only several embodiments arranged in accordance with thedisclosure and are, therefore, not to be considered limiting of itsscope, the disclosure will be described with additional specificity anddetail through use of the accompanying drawings, in which:

FIG. 1 is a conceptual chemical structure of a graphene monolayer;

FIG. 2 is a conceptual representation of a photomicrograph of defects ingraphene grown on 99.8% pure copper;

FIG. 3 is a conceptual representation of a photomicrograph of defects ingraphene grown on high purity 99.999% copper as described herein;

FIG. 4A is a conceptual illustration of operations in growing grapheneon high purity copper as described herein;

FIG. 4B is a graph outlining an example of graphene growth conditions;

FIG. 5 is a flow diagram showing example operations that may be used forcarrying out the described method of growing graphene on high puritycopper;

FIG. 6 is a block diagram of an automated machine that may be used forcarrying out the described method of growing graphene on high puritycopper;

FIG. 7 illustrates a general purpose computing device that may be usedto control the automated machine of FIG. 6 or similar equipment incarrying out the described method of growing graphene on high puritycopper; and

FIG. 8 illustrates a block diagram of an example computer programproduct that may be used to control the automated machine of FIG. 7 orsimilar equipment in carrying out the described method of growinggraphene on high purity copper,

all arranged in accordance with at least some embodiments describedherein.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof. In the drawings,similar symbols typically identify similar components, unless contextdictates otherwise. The illustrative embodiments described in thedetailed description, drawings, and claims are not meant to be limiting.Other embodiments may be utilized, and other changes may be made,without departing from the spirit or scope of the subject matterpresented herein. It will be readily understood that the aspects of thepresent disclosure, as generally described herein, and illustrated inthe Figures, can be arranged, substituted, combined, separated, anddesigned in a wide variety of different configurations, all of which areexplicitly contemplated herein.

This disclosure is generally drawn, inter alia, to compositions,methods, apparatus, systems, devices, and/or computer program productsrelated to improving the growth of graphene on copper by chemical vapordeposition.

Briefly stated, technologies are presented for growing graphene bychemical vapor deposition (CVD) on a high purity copper surface. Thesurface may be prepared by deposition of a high purity copper layer,e.g., 99.999% pure, on a lower purity copper substrate, e.g., 99.8%pure, using deposition processes such as sputtering, evaporation,electroplating, or CVD. The high purity copper layer can have a higherpercent purity than the lower purity copper substrate. The deposition ofthe high purity copper layer may be followed by a thermal treatment tofacilitate grain growth. Use of the high purity copper layer incombination with the lower purity copper substrate may provide thermalexpansion matching, compatibility with copper etch removal, or reductionof contamination, producing fewer graphene defects compared to directdeposition on a lower purity substrate at substantially less expensethan deposition approaches using a high purity copper foil substrate.

FIG. 1 is a conceptual chemical structure of a graphene monolayer 100,showing a one-atom-thick planar sheet of sp2 carbon atoms 102 that aredensely packed in a hexagonal crystal lattice. Graphene is a basicstructural element of carbon materials such as graphite, carbonnanotubes and fullerenes. Graphene monolayer 100 is an idealizedstructure, without defects. Idealized graphene is expected to have manyinteresting and useful properties, such as electrical conductivity,thermal conductivity, transparency, and mechanical stiffness. However,these properties may depend at least in part how well a particulargraphene monolayer conforms to the idealized structure depicted forgraphene monolayer 100. For example, ab initio calculations have beenreported which show that a graphene monolayer may be thermodynamicallyless stable than fullerene structures if its size is less than about 20nanometers in diameter or about 6000 atoms, but the graphene monolayermay be thermodynamically more stable compared to fullerene structuressizes larger than about 24,000 carbon atoms. For at least these reasons,the reduction of defects in graphene may be of great interest.

FIG. 2 is a conceptual representation of a photomicrograph of variousdefects in a sample of graphene grown on 99.8% pure copper. FIG. 2 showsa diagram 200 of a number of defects that may be visually characterizedas dark spots (202), light spots (204), multilayer graphene (206 & 208),and defective streaks (210).

FIG. 3 is a conceptual representation of a photomicrograph of variousdefects in a sample of graphene grown on 99.999% pure copper. FIG. 3shows a diagram 300 of fewer spot defects 202 and 304. There are fewerdefects overall, for example, none of the multilayer graphene ordefective streaks 206, 208 and 210 found in FIG. 2 are observed in FIG.3. It has been documented that CVD graphene grown on a 99.8% pure coppersubstrate, such as in FIG. 2, may produce more than ten times the numberof defects compared to CVD graphene grown on a 99.999% pure coppersubstrate, such as in FIG. 3. Unfortunately 99.999% pure copper may costconsiderably more than 99.8% copper, between ten to one hundred timesmore at current prices. Moreover, under known approaches, the copper maybe etched away in the fabrication process, so the value of the highpurity copper may be lost even though the copper may be reclaimed.

FIG. 4A is a conceptual illustration of operations in growing grapheneon high purity copper as described herein. In a diagram 400A, a sampleof low-purity copper 402 may be used in the form of a slab, or a foillaid on a further substrate.

The low-purity copper 402 may be cleaned in operation 401, for exampleusing sputter cleaning, acid etching, solvent rinsing/degreasing,electropolishing, chemical mechanical polishing, or other suitablecleaning processes. Suitable acid etching processes may employ, forexample, carboxylic acids such as acetic acid, citric acid, maleic acid,oxalic acid, or glycolic acid. Suitable solvents may include, forexample, alkanes such as pentane, hexane, or cyclohexane; halogenatedsolvents such as dichloromethane, trichloroethylene, orchlorofluorocarbons; aromatic solvents such as benzene, toluene, orxylenes; alcohols such as methanol, ethanol, or 2-propanol; or ketonessuch as acetone or methyl ethyl ketone.

Next, in operation 403, high-purity copper layer 404 may be laid onlow-purity copper 402, for example by sputtering, evaporation,electroplating, chemical vapor deposition (CVD), or other suitable highpurity deposition processes. By using a thin film of high purity coppersuch as high-purity copper layer 404 on top of standard purity copperfoil such as low-purity copper 402, higher quality graphene may be grownon high purity copper while reducing the amount of high purity copperused. Use of the low purity copper 402 may improve interfacial bondingwith the high-purity copper layer 404, for example by matching thermalexpansion coefficients at the interface. Also, the same or similarcopper etch process may be used for removal of copper from the graphene.

The high-purity copper layer 404, as deposited, may have a small grainsize. Grain boundaries may produce lower quality graphene such as duringa CVD growth operation. Accordingly, in operation 405, the high-puritycopper layer 404 may be thermally annealed, which may lead to graingrowth and reduction in grain boundary density. Suitable thermalannealing conditions may be selected to promote grain growth, avoidcopper vaporization, and avoid surface oxidation of the copper. Suitablethermal annealing conditions may include heating to an annealingtemperature of about 750° C. to about 1000° C., or in some examplesabout 800° C. to about 900° C. Specific examples of annealingtemperatures include about 750° C., about 800° C., about 850° C., about900° C., about 950° C., about 1000° C., and ranges between any two ofthese values. Suitable thermal annealing conditions may also includeheating in the absence of oxygen, for example in a vacuum. In otherexamples, a suitable atmosphere for thermal annealing may include one ormore noble gases, e.g., helium, neon, argon, or xenon, in aconcentration of about 90 mole % to about 99 mole %. A suitableatmosphere for thermal annealing may also include hydrogen in aconcentration of about 1 mole % to about 10 mole %. In a specificexample, a thermal annealing operation may include heating to about 800°C. to about 900° C. in an atmosphere of 95 mole % argon and 5 mole %hydrogen.

In operation 407, a graphene layer 406 may be deposited on thehigh-purity copper layer 404. Any suitable approach for growing graphenemay be employed, for example, the various approaches of growing graphenevia CVD. One specific example of graphene growth is outlined in thegraph depicted in FIG. 4B. The combination of copper layers 402 and 404may be placed in a CVD chamber under about 2 standard cubic centimetersper minute (sccm) of hydrogen gas at a pressure of about 40 milliTorr.The combined copper layers 402/404 may be heated to a temperature ofabout 1000° C. over a period of about 45 minutes, and the temperaturemay be allowed to stabilize, for example for another 15 minutes. A CVDgrowth gas such as methane may be admitted, for example, at a flow ofabout 35 sccm to reach a total chamber pressure of about 500 milliTorr.The hydrogen flow may be continued at about 2 sccm. The graphene may beallowed to grow for a period of time, for example about 30 minutes. TheCVD chamber heater may then be shut off, and the CVD chamber may beallowed to cool to ambient temperature, for example over about 50minutes. During cooling, the gas flow may be maintained at about 2 sccmof hydrogen and about 35 sccm of methane, while the pressure may bemaintained, for example at about 500 milliTorr.

The layers of low-purity copper 402 and high-purity copper 404 may eachbe characterized by average thickness. For example, the low-puritycopper 402 may be in any suitable thickness from about 3 micrometers toabout 300 micrometers. Specific thickness examples include about 3micrometers, about 10 micrometers, about 25 micrometers, about 50micrometers, about 100 micrometers, about 150 micrometers, about 200micrometers, about 250 micrometers, about 300 micrometers, and rangesbetween any two of these values. As an example, a suitable thickness forsmall area samples may be about 25 micrometers thick. For ease ofhandling, larger samples may employ thicker layers, for example, 100micrometers thick. The high-purity copper 404 may be in any suitablethickness from a single atomic monolayer to about 25 micrometers thick.For example, the high-purity copper 404 may be from about 0.1micrometers to about 1 micrometer in thickness. Specific thicknessexamples include about 0.1 micrometers, about 0.2 micrometers, about 0.3micrometers, about 0.4 micrometers, about 0.5 micrometers, about 0.6micrometers, about 0.7 micrometers, about 0.8 micrometers, about 0.9micrometers, about 1.0 micrometers, and ranges between any two of thesevalues. In addition, the low-purity copper 402 may have a greateraverage thickness compared to the high-purity copper 404.

The layers of low-purity copper 402 and high-purity copper 404 may eachbe characterized by copper percentage by weight. The high-purity copper404 may have a greater copper percentage by weight compared to thelow-purity copper 402, e.g., by at least about 0.1%. For example, thehigh-purity copper 404 may have a copper percentage by weight of about99.9% or more. In other examples, the low-purity copper 402 may have acopper percentage by weight of about 99.9% or less. As a specificexample, the high-purity copper 404 may be 99.999% copper by weight andthe low-purity copper 302 may be about 99.8% copper by weight.

The layers of low-purity copper 402 and high-purity copper 404 may eachbe characterized by oxygen percentage by weight. As used herein, “oxygenpercentage by weight” includes oxygen present in any form, for example,dissolved oxygen or precipitated oxygen compounds of metals or otherelements. The oxygen percentage by weight may be expressed as anequivalent parts per million (ppm) by weight, for example, 0.01% byweight is equivalent to 100 ppm by weight. In various examples, theoxygen percentage by weight of the high-purity copper 404 is about thesame or less compared to the low-purity copper 402. The low puritycopper 402 may be characterized by an oxygen percentage by weight ofless than 1%, in some examples less than about 0.2%. The low puritycopper 402 may be characterized by an oxygen percentage by weight ofless than 0.0028% or 28 ppm, in some examples less than about 0.001% or10 ppm.

Copper may also be characterized by dissolved oxygen percentage byweight, e.g., high purity copper 404 may be saturated in dissolvedoxygen at the annealing temperature. For example, at 1000° C., thesaturated solubility of oxygen in copper, e.g., high purity copper 404,is 0.0028% by weight or 28 ppm by weight. Without wishing to be bound bytheory, saturating the high purity copper layer 404 in dissolved oxygenmay block further diffusion of oxygen from the low-purity copper layer402 to the high-purity copper layer 404, which may reduce graphenedefect formation. It is not currently known whether typical graphenedefects correlate to any typical impurity in 99.8% copper, however, itis known that common impurities in 99.8% copper may include oxygen,nickel, and iron, of which oxygen is generally the single greatestimpurity. It is believed that nickel and iron may be less likely tocause graphene defects, at least at low concentrations, because nickeland iron may catalyze the formation of graphene under CVD conditions. Itis also believed that the presence of oxygen may interfere with thecatalytic formation of graphene in CVD, which may lead to the observeddefects.

In further examples, the high-purity copper 404 may be saturated inoxygen at the annealing temperature and/or at the graphene growthtemperature. Likewise, the low-purity copper 402 may be saturated inoxygen at the annealing temperature and/or at the graphene growthtemperature. In further examples, both the high-purity copper 404 andthe low-purity copper 402 may be saturated in oxygen at the annealingand graphene growth temperatures.

Example embodiments may also include methods of manufacturing grapheneas described herein. These methods may be implemented in any number ofways, including the structures described herein. One such way may be bymachine operations, of devices of the type described in the presentdisclosure. Another optional way may be for one or more of theindividual operations of the methods to be performed in conjunction withone or more human operators performing some of the operations whileother operations may be performed by machines. The various humanoperators need not be collocated with each other, and instead eachoperated can be located about one or more machines that perform aportion of the operations. In other examples, the human interaction maybe automated such as by pre-selected criteria that may be machineautomated.

FIG. 5 is a flow diagram showing operations that may be used inmanufacturing graphene, arranged in accordance with at least someembodiments described herein. A process of manufacturing graphene asdescribed herein may include one or more operations, functions oractions as is illustrated by one or more of operations 522, 524, 526,528, 530, and/or 532. An example method of manufacturing graphene asdescribed herein may be operated by a controller device 510, which maybe embodied as computing device 700 in FIG. 7 or a special purposecontroller such as manufacturing controller 690 of FIG. 6, or similardevices configured to execute instructions stored in computer-readablemedium 520 for controlling the performance of the method.

Some example processes may begin with operation 522, “PROVIDE A COPPERSUBSTRATE THAT INCLUDES TWO CONTACTING LAYERS WITH THE COPPER PERCENTAGEOF THE FIRST LAYER GREATER THAN THE COPPER PERCENTAGE OF THE SECONDLAYER.” Operation 522 may be performed, for example, by manual orautomatic loading of the copper substrate sample into a sample stage, orby preparing the copper substrate as provided in optional operations524, 526, and/or 528.

For example, operation 522 may be followed by operation 524, “PROVIDETHE FIRST LAYER.” Operation 524 may include manual or automatic loadingof the first copper layer into a sample stage.

Operation 524 may be followed by operation 526, “CLEAN A SURFACE OF THEFIRST LAYER.” Operation 526 may include contacting the surface of thefirst layer with a cleaning agent from a cleaning source. For example,the cleaning source may include a reservoir of a cleaning agent and anapplicator for contacting the cleaning agent to the surface of the firstlayer. The cleaning source may include a liquid applicator and acleaning agent reservoir. For example, acid etching of the surface ofthe first layer may be conducted by applying an acid from the cleaningagent source such as acetic acid, citric acid, maleic acid, oxalic acid,or glycolic acid. The cleaning agent source may also supply a solventfor cleaning, for example: alkanes such as pentane, hexane, orcyclohexane; halogenated solvents such as dichloromethane,trichloroethylene, or chlorofluorocarbons; aromatic solvents such asbenzene, toluene, or xylenes; or alcohols such as methanol, ethanol, or2-propanol. The cleaning source may also include a sputter source forsputter cleaning of the surface of the first layer.

Operation 526 may be followed by operation 528, “DEPOSIT THE SECONDLAYER ON THE SURFACE OF THE FIRST COPPER LAYER TO FORM THE COPPERSUBSTRATE.” Operation 526 may be conducted by any copper depositionsource suitable for high purity deposition, for example, by sputtering,evaporation, electroplating, chemical vapor deposition (CVD), or otherhigh purity deposition processes.

Operations 522, 524, 526 and 528 may be followed by operation 530,“THERMALLY ANNEAL THE COPPER SUBSTRATE”. This may be accomplished usinga heater and may be conducted in an environment substantially free ofoxygen, for example, a vacuum, or a partial pressure of one or morenoble gases and/or hydrogen, as described herein.

Operation 530 may be followed by operation 532, “GROW A GRAPHENEMONOLAYER VIA CHEMICAL VAPOR DEPOSITION ON THE SECOND LAYER.” Thegraphene may be grown using any suitable approach for growing graphenevia CVD, for example, the CVD methods of growing graphene describedherein. The graphene is grown in at least a monolayer, and additionalgraphene layers may be grown.

The operations included in the process of FIG. 5 described above are forillustration purposes. A process of growing graphene as described hereinmay be implemented by similar processes with fewer or additionaloperations. In some examples, the operations may be performed in adifferent order. In some other examples, various operations may beeliminated. In still other examples, various operations may be dividedinto additional operations, or combined together into fewer operations.Although illustrated as sequentially ordered operations, in someimplementations the various operations may be performed in a differentorder, or in some cases various operations may be performed atsubstantially the same time. For example, any other similar process maybe implemented with fewer, different, or additional operations so longas such similar processes grow graphene using the copper substrate.

FIG. 6 is a block diagram of a manufacturing system 600 that may be usedfor of growing graphene and preparing the copper substrate as describedherein using the process operations outlined in FIG. 5, arranged inaccordance with at least some embodiments described herein. Asillustrated in FIG. 6, a manufacturing controller 690 may be coupled tothe machines that may be employed to carry out the operations describedin FIG. 5, for example: a deposition chamber 692; a sample stage 693;one or more sensors 694 such as temperature sensors or copper thicknesssensors; a heater 695; a copper deposition source 696; a cleaning agentsource 697; a gas source 698; and an optional roll to roll applicator699.

Manufacturing controller 690 may be operated by human control, by aremote controller 670 via network 610, or by machine executedinstructions such as might be found in a computer program. Dataassociated with controlling the different processes of manufacturinggraphene may be stored at and/or received from data stores 680. Further,the individual elements of manufacturing system 600 may be implementedas any suitable device configured in any suitable fashion for carryingout the operations described herein. For example, sample stage 620 maybe stationary or may include one or more moving functions, such astranslation in zero, one, two, or three perpendicular axes, rotation inone, two, or three perpendicular axes, or combinations thereof. Suchmoving functions may be provided by motors, linear actuators, orpiezoelectric actuators. Likewise, copper deposition source 696 may beconfigured for any approach for depositing high purity copper, such asby sputtering, evaporation, atomic or chemical vapor deposition, or highpurity electroplating. Similarly, cleaning agent source 697 may beconfigured for any suitable approach for cleaning a copper surface, forexample, a liquid applicator and a cleaning agent reservoir suitable forsolvents or acid etchants, or a sputter cleaner. Further, gas source 698may be any combination of gas reservoirs, valves, pressure sensors, ormanifolds capable of providing process gases, such as noble gases,hydrogen, or graphene CVD source gases such as methane. Moreover,optional roll to roll applicator 699 may be desirable for large areaapplications or other situations where continuous preparation of thecopper layers and CVD deposition may be conducted without additionalhandling or exposure of the substrate to atmospheric gases.

FIG. 7 illustrates a general purpose computing device that may be usedto control the manufacturing system 600 of FIG. 6 or similarmanufacturing equipment in growing graphene, arranged in accordance withat least some embodiments described herein. In a basic configuration702, referring to the components within the dashed line, computingdevice 700 typically may include one or more processors 704 and a systemmemory 706. A memory bus 708 may be used for communicating betweenprocessor 704 and system memory 706.

Depending on the desired configuration, processor 704 may be of any typeincluding but not limited to a microprocessor (μP), a microcontroller(μC), a digital signal processor (DSP), or any combination thereof.Processor 704 may include one more levels of caching, such as a cachememory 712, a processor core 714, and registers 716. Processor core 714may include an arithmetic logic unit (ALU), a floating point unit (FPU),a digital signal processing core (DSP Core), or any combination thereof.An example memory controller 718 may also be used with processor 704, orin some implementations memory controller 718 may be an internal part ofprocessor 704.

Depending on the desired configuration, system memory 706 may be of anytype including but not limited to volatile memory (such as RAM),non-volatile memory (such as ROM, flash memory, etc.) or any combinationthereof. System memory 706 may include an operating system 720, one ormore manufacturing control applications 722, and program data 724.Manufacturing control application 722 may include a control module 726that may be arranged to control manufacturing system 600 of FIG. 6 andany other processes, methods and functions as discussed above. Programdata 724 may include, among other data, material data 728 forcontrolling various aspects of the manufacturing system 600.

Computing device 700 may have additional features or functionality, andadditional interfaces to facilitate communications between basicconfiguration 702 and any required devices and interfaces. For example,a bus/interface controller 730 may be used to facilitate communicationsbetween basic configuration 702 and one or more data storage devices 732via a storage interface bus 734. Data storage devices 732 may beremovable storage devices 736, non-removable storage devices 738, or acombination thereof. Examples of removable storage and non-removablestorage devices may include magnetic disk devices such as flexible diskdrives and hard-disk drives (HDD), optical disk drives such as compactdisk (CD) drives or digital versatile disk (DVD) drives, solid statedrives (SSD), and tape drives to name a few. Example computer storagemedia may include volatile and nonvolatile, removable and non-removablemedia implemented in any method or technology for storage ofinformation, such as computer readable instructions, data structures,program modules, or other data.

System memory 706, removable storage devices 736 and non-removablestorage devices 738 may be examples of computer storage media. Computerstorage media may include, but is not limited to, RAM, ROM, EEPROM,flash memory or other memory technology, CD-ROM, digital versatile disks(DVD) or other optical storage, magnetic cassettes, magnetic tape,magnetic disk storage or other magnetic storage devices, or any othermedium which may be used to store the desired information and which maybe accessed by computing device 700. Any such computer storage media maybe part of computing device 700.

Computing device 700 may also include an interface bus 740 forfacilitating communication from various interface devices (e.g., outputdevices 742, peripheral interfaces 744, and communication devices 766)to basic configuration 702 via bus/interface controller 730. Outputdevices 742 may include a graphics processing unit 748 and an audioprocessing unit 750, which may be configured to communicate to variousexternal devices such as a display or speakers via one or more A/V ports752. Example peripheral interfaces 744 include a serial interfacecontroller 754 or a parallel interface controller 756, which may beconfigured to communicate with external devices such as input devices(e.g., keyboard, mouse, pen, voice input device, touch input device,etc.) or other peripheral devices (e.g., printer, scanner, etc.) via oneor more I/O ports 758. A communication device 766 may include a networkcontroller 760, which may be arranged to facilitate communications withone or more other computing devices 762 over a network communicationlink via one or more communication ports 764.

The network communication link may be one example of a communicationmedia. Communication media may typically be embodied by computerreadable instructions, data structures, program modules, or other datain a modulated data signal, such as a carrier wave or other transportmechanism, and may include any information delivery media. A “modulateddata signal” may be a signal that has one or more of its characteristicsset or changed in such a manner as to encode information in the signal.By way of example, and not limitation, communication media may includewired media such as a wired network or direct-wired connection, andwireless media such as acoustic, radio frequency (RF), microwave,infrared (IR) and other wireless media. The term computer readable mediaas used herein may include both storage media and communication media.

Computing device 700 may be implemented as a portion of a physicalserver, virtual server, a computing cloud, or a hybrid device thatinclude any of the above functions. Computing device 700 may also beimplemented as a personal computer including both laptop computer andnon-laptop computer configurations. Moreover computing device 700 may beimplemented as a networked system or as part of a general purpose orspecialized server.

Networks for a networked system including computing device 700 maycomprise any topology of servers, clients, switches, routers, modems,Internet service providers, and any appropriate communication media(e.g., wired or wireless communications). A system according toembodiments may have a static or dynamic network topology. The networksmay include a secure network such as an enterprise network (e.g., a LAN,WAN, or WLAN), an unsecure network such as a wireless open network(e.g., IEEE 802.11 wireless networks), or a world-wide network such(e.g., the Internet). The networks may also comprise a plurality ofdistinct networks that may be adapted to operate together. Such networksmay be configured to provide communication between the nodes describedherein. By way of example, and not limitation, these networks mayinclude wireless media such as acoustic, RF, infrared and other wirelessmedia. Furthermore, the networks may be portions of the same network orseparate networks.

FIG. 8 illustrates a block diagram of an example computer programproduct that may be used to control the automated machine of FIG. 6 orsimilar manufacturing equipment in manufacturing graphene, arranged inaccordance with at least some embodiments described herein. In someexamples, as shown in FIG. 8, computer program product 800 may include asignal bearing medium 802 that may also include machine readableinstructions 804 that, when executed by, for example, a processor, mayprovide the functionality described above with respect to FIG. 5 throughFIG. 7. For example, referring to manufacturing controller 690, one ormore of the tasks shown in FIG. 8 may be undertaken in response tomachine readable instructions 804 conveyed to the imaging controller 690by signal bearing medium 802 to perform actions associated with growinggraphene as described herein. Some of those instructions may include,for example, one or more instructions for: “providing a copper substratethat includes two contacting layers with the copper percentage of thefirst layer greater than the copper percentage of the second layer;”“providing the first layer;” “cleaning a surface of the first layer;”“depositing the second layer on the surface of the first copper layer toform the copper substrate;” “thermally annealing the copper substrate;”or “growing a graphene monolayer via chemical vapor deposition on thesecond layer.”

In some implementations, signal bearing medium 802 depicted in FIG. 8may encompass a computer-readable medium 806, such as, but not limitedto, a hard disk drive, a Compact Disc (CD), a Digital Versatile Disk(DVD), a digital tape, memory, etc. In some implementations, signalbearing medium 802 may encompass a recordable medium 808, such as, butnot limited to, memory, read/write (R/W) CDs, R/W DVDs, etc. In someimplementations, signal bearing medium 802 may encompass acommunications medium 810, such as, but not limited to, a digital and/oran analog communication medium (e.g., a fiber optic cable, a waveguide,a wired communications link, a wireless communication link, etc.). Forexample, computer program product 800 may be conveyed to the processor704 by an RF signal bearing medium 802, where the signal bearing medium802 may be conveyed by a communications medium 810 (e.g., a wirelesscommunications medium conforming with the IEEE 802.11 standard). Whilethe embodiments will be described in the general context of programmodules that execute in conjunction with an application program thatruns on an operating system on a personal computer, those skilled in theart will recognize that aspects may also be implemented in combinationwith other program modules.

Generally, program modules include routines, programs, components, datastructures, and other types of structures that perform particular tasksor implement particular abstract data types. Moreover, those skilled inthe art will appreciate that embodiments may be practiced with othercomputer system configurations, including hand-held devices,multiprocessor systems, microprocessor-based or programmable consumerelectronics, minicomputers, mainframe computers, and comparablecomputing devices. Embodiments may also be practiced in distributedcomputing environments where tasks may be performed by remote processingdevices that may be linked through a communications network. In adistributed computing environment, program modules may be located inboth local and remote memory storage devices.

Embodiments may be implemented as a computer-implemented process(method), a computing system, or as an article of manufacture, such as acomputer program product or computer readable media. The computerprogram product may be a computer storage medium readable by a computersystem and encoding a computer program that comprises instructions forcausing a computer or computing system to perform example process(es).The computer-readable storage medium can for example be implemented viaone or more of a volatile computer memory, a non-volatile memory, a harddrive, a flash drive, a floppy disk, or a compact disk, and comparablemedia.

Throughout this specification, the term “platform” may be a combinationof software and hardware components for providing a configurationenvironment, which may facilitate configuration of software/hardwareproducts and services for a variety of purposes. Examples of platformsinclude, but are not limited to, a hosted service executed over aplurality of servers, an application executed on a single computingdevice, and comparable systems. The term “server” generally refers to acomputing device executing one or more software programs typically in anetworked environment. However, a server may also be implemented as avirtual server (software programs) executed on one or more computingdevices viewed as a server on the network. More detail on thesetechnologies and example operations is provided below.

According to some examples, a method of manufacturing graphene isprovided. The method may include providing a copper substrate that mayinclude a first copper layer in contact with a second copper layer. Thefirst copper layer may be characterized by a first copper percentage byweight and the second copper layer may be characterized by a secondcopper percentage by weight. The second copper percentage may be greaterthan the first copper percentage. The method may also include growing agraphene monolayer via chemical vapor deposition on the second copperlayer. Providing the copper substrate may include: providing the firstcopper layer; cleaning a surface of the first copper layer; depositingthe second copper layer on the cleaned surface of the first copper layerto form the copper substrate; and thermally annealing the coppersubstrate.

In various examples of the method, the first copper layer may be furthercharacterized by a first oxygen percentage by weight; the second copperlayer may be further characterized by a second oxygen percentage byweight; and the second oxygen percentage may be about the same or lessthan the first oxygen percentage. In a dimension perpendicular to thegraphene monolayer, the first copper layer may be characterized by afirst average thickness; the second copper layer may be characterized bya second average thickness; and the second average thickness may be lessthan the first average thickness. The second average thickness may beone atomic monolayer of copper to about 25 micrometers. The firstaverage thickness may be at least about 3 micrometers.

In other examples of the method, the second copper percentage may begreater than the first copper percentage by at least about 0.1%. In someexamples, the second copper percentage may be at least about 99.9%; thefirst copper percentage may be less than about 99.9%; or the secondcopper percentage may be at least about 99.9% and the first copperpercentage may be less than about 99.9%.

In various examples of the method, the surface of the first copper layermay be cleaned by one or more of sputter cleaning, acid etching, solventrinsing, electropolishing, or chemical mechanical polishing. The secondcopper layer may be deposited on the surface of the first copper layerby one or more of sputtering, evaporation, electroplating, or chemicalvapor deposition (CVD).

In some examples of the method, thermal annealing may include heating toan annealing temperature of about 750° C. to about 1000° C. The secondcopper layer may be saturated in dissolved oxygen at the annealingtemperature. The thermal annealing may include heating in an atmospherethat includes: about 1 mole % hydrogen to about 10 mole % hydrogen, andabout 90 mole % to about 99 mole % of one or more noble gases. Thethermal annealing may include heating in an atmosphere substantiallyfree of oxygen.

According to some examples, a copper substrate for growing a graphenemonolayer is provided. The copper substrate may include a first copperlayer characterized by: a first copper percentage by weight, a firstoxygen percentage by weight, and a first thickness. The copper substratemay also include a second copper layer in contact with the first copperlayer. The second copper layer may be characterized by: a second copperpercentage by weight, a second oxygen percentage by weight, and a secondthickness. In the copper substrate, the second copper percentage may begreater than the first copper percentage; the second oxygen percentagemay be about the same or less than the first oxygen percentage; and thesecond average thickness may be less than the first average thickness.The second average thickness may be one atomic monolayer of copper toabout 25 micrometers. The first average thickness may be at least about3 micrometers. The second copper percentage may be greater than thefirst copper percentage by at least about 0.1%. In some examples, thesecond copper percentage may be at least about 99.9%; the first copperpercentage may be less than about 99.9%; or the second copper percentagemay be at least about 99.9% and the first copper percentage may be lessthan about 99.9%.

According to some examples, a graphene-copper composite is provided. Thegraphene-copper composite may include a first copper layer characterizedby: a first copper percentage by weight, a first oxygen percentage byweight, and a first thickness. The graphene-copper composite may includea second copper layer having a first surface in contact with the firstcopper layer. The second copper layer may be characterized by: a secondcopper percentage by weight, a second oxygen percentage by weight, and asecond thickness. The graphene-copper composite may also include agraphene monolayer in contact with a second surface of the second copperlayer. In the graphene-copper composite, the second copper percentagemay be greater than the first copper percentage; the second oxygenpercentage may be about the same or less than the first oxygenpercentage; and the second average thickness may be less than the firstaverage thickness. The second average thickness may be one atomicmonolayer of copper to about 25 micrometers. The first average thicknessmay be at least about 3 micrometers. The second copper percentage may begreater than the first copper percentage by at least about 0.1%. In someexamples, the second copper percentage may be at least about 99.9%; thefirst copper percentage may be less than about 99.9%; or the secondcopper percentage may be at least about 99.9% and the first copperpercentage may be less than about 99.9%.

According to some examples, a system for manufacturing a coppersubstrate for growing graphene is provided. The system may include adeposition chamber; a sample stage configured to hold a copper substratein the deposition chamber; a copper deposition source; a cleaning agentsource configured to direct cleaning agent to the copper substrate heldby the sample stage; a sensor configured to determine a thickness of alayer deposited by the copper deposition source; a heater configured toheat the copper substrate held by the sample stage to an annealingtemperature of about 750° C. to about 1000° C.; a gas source configuredto provide a thermal annealing gas to the copper substrate held by thesample stage; and a microprocessor. The microprocessor may be coupled tothe deposition chamber, the sample stage, the copper deposition source,the cleaning agent source, the sensor, and the heater. Themicroprocessor may be programmable to: employ the sample stage to hold afirst copper layer in the deposition chamber; employ the cleaning agentsource to direct cleaning agent to the first copper layer; employ thecopper deposition source and the sensor to deposit a second copper layeron the first copper layer, wherein the second copper layer may bethinner compared to the first copper layer, and employ the heater andthe gas source to thermally anneal the first copper layer at the coppersubstrate. The cleaning agent source may be configured to provide one ormore of sputter cleaning, acid etching, solvent rinsing,electropolishing, or chemical mechanical polishing. The copperdeposition source may be configured to deposit copper by one or more ofsputtering, evaporation, electroplating, or chemical vapor deposition(CVD).

In various examples, the system may further include a chemical vaporsource configured to provide one or more chemical vapor depositionprecursors for forming graphene, wherein the microprocessor may beprogrammable to employ the chemical vapor source to grow a graphenemonolayer at the second copper layer using the one or more chemicalvapor deposition precursors for forming graphene.

In various examples of the system, the first copper layer may becharacterized by a first oxygen percentage by weight and themicroprocessor may be further programmable to employ the copperdeposition source to deposit the second copper layer at a second oxygenpercentage by weight that is about the same or less than the firstoxygen percentage. In some examples of the system, in a dimensionperpendicular to the graphene monolayer, the first copper layer ischaracterized by a first average thickness, and the microprocessor maybe further programmable to employ the copper deposition source and thesensor to deposit the second copper layer at a second average thicknessthat is less than the first average thickness. The microprocessor may befurther programmable to employ the copper deposition source and thesensor to deposit the second copper layer such that the second averagethickness is one atomic monolayer of copper to about 25 micrometers.

In some examples of the system, the microprocessor may be programmableto employ the heater and the gas source to thermally anneal the firstcopper layer at an annealing temperature of about 750° C. to about 1000°C. The microprocessor may be programmable to employ the heater and thegas source to thermally anneal the first copper layer in an atmospherethat includes about 1 mole % hydrogen to about 10 mole % hydrogen, andabout 90 mole % to about 99 mole % of one or more noble gases. Themicroprocessor may be programmable to employ the heater and the gassource to thermally anneal the first copper layer in an atmospheresubstantially free of oxygen.

According to some examples, a computer-readable storage medium havinginstructions stored thereon for manufacturing a copper substrate forgrowing graphene is provided. The instructions may include providing afirst copper layer; cleaning a surface of the first copper layer,depositing a second copper layer on the cleaned surface of the firstcopper layer to form the copper substrate; and thermally annealing thecopper substrate. The first copper layer may be characterized by: afirst copper percentage by weight, a first oxygen percentage by weight,and a first thickness. The second copper layer may be characterized by:a second copper percentage by weight, a second oxygen percentage byweight, and a second thickness. The second copper layer may be depositedsuch that one or more of: the second copper percentage may be greaterthan the first copper percentage, the second oxygen percentage may beabout the same or less than the first oxygen percentage, and/or thesecond average thickness may be less than the first average thickness.The surface of the first copper layer may be cleaned by one or more ofsputter cleaning, acid etching, solvent rinsing, electropolishing, orchemical mechanical polishing. The second copper layer may be depositedon the surface of the first copper layer by sputtering, evaporation,electroplating, or chemical vapor deposition (CVD). The second copperlayer may be saturated in dissolved oxygen at the annealing temperature.

In various examples of the computer-readable storage medium, theinstructions for thermal annealing may include heating to an annealingtemperature of about 750° C. to about 1000° C. The instructions forthermal annealing may also include heating in an atmosphere thatincludes about 1 mole % hydrogen to about 10 mole % hydrogen, and about90 mole % to about 99 mole % of one or more noble gases. The thermalannealing may include heating in an atmosphere substantially free ofoxygen.

In some examples of the computer-readable storage medium, theinstructions may further include growing a graphene monolayer viachemical vapor deposition on the second copper layer.

Example 1A Preparation of 99.8% Parity Copper Surface

A 50×50 millimeter square of 99.8% copper foil may be prepared (100micrometers thick, catalog #12816, Sigma-Aldrich, St. Louis Mo.). The99.8% copper foil may be degreased by washing in acetone (≧99.9%,catalog #650501, Sigma-Aldrich, St. Louis Mo.), etched in 0.1 M aceticacid (≧99.99%, catalog #338826, Sigma-Aldrich, St. Louis Mo., diluted indistilled, deionized water to 0.1 M) at 25° C. for 5 minutes, washedwith distilled, deionized water, and dried. The 99.8% copper foil maythen be affixed to a machined stainless steel sample holder, placed in achamber of a sputtering apparatus (Perkin-Elmer 4400 RF SputteringPlasma Deposition System, Perkin-Elmer, Waltham Mass.), evacuated toabout 4×10⁻⁸ Pascals base pressure, and sputter cleaned for 3 min at 0.2milliAmperes with Ar ions accelerated at 500 V.

Example 1B Preparation of 99.999% Purity Copper Surface

A 99.8% copper foil sample may be provided under ultra-high vacuumconditions (about 4×10⁻⁸ Pascals base pressure) in the sputteringapparatus as described in Example 1A. The sputtering apparatus may beoperated at a deposition temperature of 100° C., 200 W working power,and a deposition rate of approximately 1.2 nanometers/second. At thesame time, the sample holder may be rotated at 100 rotations per minuteto deposit 99.999% pure copper on the in a thickness of 0.1 micrometerson the 99.8% copper foil to form a two-layer copper composition. Thetwo-layer copper composition may then be removed from the sputteringapparatus and heated in a fused silica tube furnace to a temperature of850° C. for 30 minutes under an atmosphere of 95% Ar/5% H₂ atatmospheric pressure. The fused silica tube furnace may be cooled toprovide an annealed two-layer copper substrate suitable for growinggraphene as described herein.

Example 2A Preparation of Graphene on the 99.8% Purity Copper Surface

A sample of the 99.8% pure copper as cleaned in Example 1A may be placedin the fused silica tube furnace, configured as a chemical vapordeposition (CVD) chamber. Hydrogen gas may be supplied at 2 standardcubic centimeters per minute (sccm) at a pressure of about 40 milliTorr.The 99.8% copper foil may be heated to a temperature of about 1000° C.over a period of about 45 minutes, and the temperature may be allowed tostabilize for another 15 minutes. Methane may be admitted at a flow ofabout 35 sccm to reach a total chamber pressure of about 500 milliTorr.The hydrogen flow may be continued at about 2 sccm. The graphene may beallowed to grow on the 99.8% copper foil for about 30 minutes. The CVDchamber heater may then be shut off, and the CVD chamber may be allowedto cool to ambient temperature over about 50 minutes. During cooling,the gas flow may be maintained at about 2 sccm of hydrogen and about 35sccm of methane at a total pressure of 500 milliTorr.

Example 2B Preparation of Graphene on the 99.999% Purity Copper Surface

A sample of the annealed two-layer copper substrate produced in Example1B is placed in the CVD system with the top 99.999% copper layer exposedfor chemical vapor deposition. The CVD system may be supplied withhydrogen gas at 2 sccm at a pressure of about 40 milliTorr. The annealedtwo-layer copper substrate may be heated to a temperature of about 1000°C. over a period of about 45 minutes, and the temperature may be allowedto stabilize for another 15 minutes. Methane may be admitted at a flowof about 35 sccm to reach a total chamber pressure of about 500milliTorr. The hydrogen flow may be continued at about 2 sccm. Thegraphene may be allowed to grow on the 99.999% surface of the annealedtwo-layer copper substrate for about 30 minutes. The CVD chamber heatermay then be shut off, and the CVD chamber may be allowed to cool toambient temperature over about 50 minutes. During cooling, the gas flowmay be maintained at about 2 sccm of hydrogen and about 35 sccm ofmethane at a total pressure of 500 milliTorr.

Example 2C Comparison of Graphene Produced on High and Low PuritySurfaces

Graphene produced in Examples 2A and 2B, together with the respectiveunderlying copper substrates, may each be imaged using an opticalmicroscope. The images may be examined at a magnification of 150× andsurveyed different defect morphologies (square, triangle, circlerepresent different morphologies of the defects observed with theoptical microscope). The graphene of Example 2A, produced on the lowerpurity 99.8% copper surface, may have a defect areal density of about8000 defects per square centimeter. The graphene of Example 2B, producedon the high purity 99.999% copper surface, may have a defect arealdensity of about 1000 defects per square centimeter.

Example 3A Preparation of 99.8% Purity Copper Surface

A 25×25 millimeter square of 99.8% copper foil may be prepared (50micrometers thick, catalog #35818, Alfa Aesar, Ward Hill, Mass.). The99.8% copper foil may be degreased by washing in methanol (≧99.9%,catalog #34860, Sigma-Aldrich, St. Louis Mo.), etched in 0.1 M citricacid (99.9998%, catalog #94068, Sigma-Aldrich, St. Louis Mo., diluted indistilled, deionized water to 0.1 M) at 25° C. for 30 minutes, washedwith distilled, deionized water, and dried. The 99.8% copper foil maythen be affixed to a machined stainless steel sample holder, placed inthe sputtering apparatus, evacuated to about 4×10⁻⁸ Pascals basepressure, and sputter cleaned for 2 min at 0.2 milliAmperes with Ar ionsaccelerated at 500 V.

Example 3B Preparation of 99.999% Purity Copper Surface

A 99.8% copper foil sample may be provided under ultra-high vacuumconditions (about 4×10⁻⁸ Pascals base pressure) in the sputteringapparatus as described in Example 3A. The sputtering apparatus may beoperated at a deposition temperature of 100° C., 200 W working power,and a deposition rate of approximately 1.2 nanometers/second. At thesame time, the sample holder may be rotated at 100 rotations per minuteto deposit 99.999% pure copper on the in a thickness of 0.5 micrometerson the 99.8% copper foil to form a two-layer copper composition. Thetwo-layer copper composition may then be removed from the sputteringapparatus and heated in a fused silica tube furnace to a temperature of900° C. for 20 minutes under an atmosphere of 92.5% Ar/7.5% H₂ atatmospheric pressure. The fused silica tube furnace may be cooled toprovide an annealed two-layer copper substrate suitable for growinggraphene as described herein.

Example 4 Preparation of Graphene on the 99.999% Purity Copper Surface

A sample of the annealed two-layer copper substrate produced in Example3B is placed in the CVD system with the 0.5 micrometer 99.999% copperlayer exposed for chemical vapor deposition. The CVD system may besupplied with hydrogen gas at 2.2 sccm at a pressure of about 40milliTorr. The annealed two-layer copper substrate may be heated to atemperature of about 1025° C. over a period of about 45 minutes, and thetemperature may be allowed to stabilize for another 15 minutes. Methanemay be admitted at a flow of about 40 sccm to reach a total chamberpressure of about 500 milliTorr. The hydrogen flow may be continued atabout 2.2 sccm. The graphene may be allowed to grow on the 0.5micrometer 99.999% surface of the annealed two-layer copper substratefor about 25 minutes. The CVD chamber heater may then be shut off, andthe CVD chamber may be allowed to cool to ambient temperature over about50 minutes. During cooling, the gas flow may be reduced to about 2 sccmof hydrogen and about 35 sccm of methane at a total pressure of 450milliTorr.

Example 5A Roll to Roll Preparation of 99.8% Purity Copper Surface

A 30×1000 centimeter sheet of 99.8% copper foil may be prepared (25micrometers thick, catalog #13382, Alfa Aesar, Ward Hill, Mass.). The99.8% copper foil may be loaded lengthwise into a roll to roll handlingsystem and degreased by a cyclohexane spray (≧99.9%, catalog #650455,Sigma-Aldrich, St. Louis Mo.), etched by passing through a sonicatedtrough of 0.05 M oxalic acid (99.999%, catalog #658937, Sigma-Aldrich.St. Louis Mo., diluted in distilled, deionized water to 0.05 M),spray-washed with distilled, deionized water, and dried. The 99.8%copper foil may then be loaded in a roll to roll sputtering/CVDapparatus (KOBELCO LTD, Kobe. Japan), evacuated to about 10⁻⁷ Pascalsbase pressure, and continuously sputter cleaned at 0.2 milliAmperes withAr ions accelerated at 500 V, with the copper foil passing through thesputter zone at a rate of about 1 centimeter per minute.

Example 5B Roll to Roll Preparation of 99.999% Purity Copper Surface

A 99.8% copper foil roll may be provided under ultra-high vacuumconditions (about 10⁻⁷ Pascals base pressure) in the roll to rollsputtering apparatus as described in Example 5A. The sputteringapparatus may be operated at a deposition temperature of 100° C. and adeposition rate of approximately 2 nanometers/second. At the same time,the roll to roll apparatus may be operated to pass the copper foilthrough the deposition zone at a rate corresponding to deposition of99.999% pure copper in a thickness of 0.1 micrometers on the 99.8%copper foil to form a two-layer copper composition. The two-layer coppercomposition may then rolled through a furnace zone to a temperature of900° C. under an atmosphere of 92.5% Ar/7.5% H₂ at atmospheric pressure,at a rate corresponding to about 20 min exposure to the furnace zone.The copper foil may be cooled to provide an annealed two-layer copperroll substrate suitable for growing graphene as described herein.

Example 6 Roll to Roll Preparation of Graphene on the 99.999% PurityCopper Surface

A sample of the annealed two-layer copper roll substrate produced inExample 3B is placed in the roll-to-roll CVD system with the 0.1micrometer 99.999% copper layer exposed for chemical vapor deposition.The CVD system may be supplied with hydrogen gas at 8 sccm at a pressureof about 90 milliTorr. The annealed two-layer copper substrate may beheated to a temperature of about 1000° C. over a period of about 45minutes, and the temperature may be allowed to stabilize for another 15minutes. Methane may be admitted at a flow of about 24 sccm to reach atotal chamber pressure of about 450 milliTorr. The hydrogen flow may becontinued at about 8 sccm. The graphene may be allowed to grow on the0.1 micrometer 99.999% surface of the annealed two-layer coppersubstrate at a roll rate corresponding to about 25 minutes in the CVDdeposition zone. The copper substrate may be rolled through a coolinggradient zone under hydrogen gas flow at 8 sccm until ambienttemperature is reached. The result is a monolayer coating of graphene onthe two-layer copper roll substrate.

The terms “a” and “an” as used herein mean “one or more” unless thesingular is expressly specified. For example, reference to “a base” mayinclude a mixture of two or more bases, as well as a single base.

As used herein, “about” will be understood by persons of ordinary skillin the art and will vary to some extent depending upon the context inwhich it is used. If there are uses of the term which are not clear topersons of ordinary skill in the art, given the context in which it isused, “about” will mean up to, plus or minus 10% of the particular term.

As used herein, the terms “optional” and “optionally” mean that thesubsequently described circumstance may or may not occur, so that thedescription includes instances where the circumstance occurs andinstances where it does not.

There is little distinction left between hardware and softwareimplementations of aspects of systems; the use of hardware or softwareis generally (but not always, in that in certain contexts the choicebetween hardware and software may become significant) a design choicerepresenting cost vs. efficiency tradeoffs. There are various vehiclesby which processes and/or systems and/or other technologies describedherein may be effected (e.g., hardware, software, and/or firmware), andthat the preferred vehicle will vary with the context in which theprocesses and/or systems and/or other technologies are deployed. Forexample, if an implementer determines that speed and accuracy areparamount, the implementer may opt for a mainly hardware and/or firmwarevehicle: if flexibility is paramount, the implementer may opt for amainly software implementation; or, yet again alternatively, theimplementer may opt for some combination of hardware, software, and/orfirmware.

The foregoing detailed description has set forth various embodiments ofthe devices and/or processes via the use of block diagrams, flowcharts,and/or examples, Insofar as such block diagrams, flowcharts, and/orexamples contain one or more functions and/or operations, it will beunderstood by those within the art that each function and/or operationwithin such block diagrams, flowcharts, or examples may be implemented,individually and/or collectively, by a wide range of hardware, software,firmware, or virtually any combination thereof. In one embodiment,several portions of the subject matter described herein may beimplemented via Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs), digital signal processors (DSPs), orother integrated formats. However, those skilled in the art willrecognize that some aspects of the embodiments disclosed herein, inwhole or in part, may be equivalently implemented in integratedcircuits, as one or more computer programs running on one or morecomputers (e.g., as one or more programs running on one or more computersystems), as one or more programs running on one or more processors(e.g. as one or more programs running on one or more microprocessors),as firmware, or as virtually any combination thereof, and that designingthe circuitry and/or writing the code for the software and/or firmwarewould be well within the skill of one of skill in the art in light ofthis disclosure.

The present disclosure is not to be limited in terms of the particularembodiments described in this application, which are intended asillustrations of various aspects. Many modifications and variations maybe made without departing from its spirit and scope, as will be apparentto those skilled in the art. Functionally equivalent methods andapparatuses within the scope of the disclosure, in addition to thoseenumerated herein, will be apparent to those skilled in the art from theforegoing descriptions. Such modifications and variations are intendedto fall within the scope of the appended claims. The present disclosureis to be limited only by the terms of the appended claims, along withthe full scope of equivalents to which such claims are entitled. It isto be understood that this disclosure is not limited to particularmethods, systems, or components, which can, of course, vary. It is alsoto be understood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting.

In addition, those skilled in the art will appreciate that themechanisms of the subject matter described herein are capable of beingdistributed as a program product in a variety of forms, and that anillustrative embodiment of the subject matter described herein appliesregardless of the particular type of signal bearing medium used toactually carry out the distribution. Examples of a signal bearing mediuminclude, but are not limited to, the following: a recordable type mediumsuch as a floppy disk, a hard disk drive, a Compact Disc (CD), a DigitalVersatile Disk (DVD), a digital tape, a computer memory, etc.; and atransmission type medium such as a digital and/or an analogcommunication medium (e.g., a fiber optic cable, a waveguide, a wiredcommunications link, a wireless communication link, etc.).

Those skilled in the art will recognize that it is common within the artto describe devices and/or processes in the fashion set forth herein,and thereafter use engineering practices to integrate such describeddevices and/or processes into data processing systems. That is, at leasta portion of the devices and/or processes described herein may beintegrated into a data processing system via a reasonable amount ofexperimentation. Those having skill in the art will recognize that atypical data processing system generally includes one or more of asystem unit housing, a video display device, a memory such as volatileand non-volatile memory, processors such as microprocessors and digitalsignal processors, computational entities such as operating systems,drivers, graphical user interfaces, and applications programs, one ormore interaction devices, such as a touch pad or screen, and/or controlsystems including feedback loops.

A typical manufacturing system may be implemented utilizing any suitablecommercially available components, such as those typically found in datacomputing/communication and/or network computing/communication systems.The herein described subject matter sometimes illustrates differentcomponents contained within, or coupled together with, different othercomponents. It is to be understood that such depicted architectures aremerely exemplary, and that in fact many other architectures may beimplemented which achieve the same functionality. In a conceptual sense,any arrangement of components to achieve the same functionality iseffectively “associated” such that the desired functionality isachieved. Hence, any two components herein combined to achieve aparticular functionality may be seen as “associated with” each othersuch that the desired functionality is achieved, irrespective ofarchitectures or intermediate components. Likewise, any two componentsso associated may also be viewed as being “operably connected”, or“operably coupled”, to each other to achieve the desired functionality,and any two components capable of being so associated may also be viewedas being “operably couplable”, to each other to achieve the desiredfunctionality. Specific examples of operably couplable include but arenot limited to physically connectable and/or physically interactingcomponents and/or wirelessly interactable and/or wirelessly interactingcomponents and/or logically interacting and/or logically interactablecomponents.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity.

It will be understood by those within the art that, in general, termsused herein, and especially in the appended claims (e.g., bodies of theappended claims) are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”etc.). It will be further understood by those within the art that if aspecific number of an introduced claim recitation is intended, such anintent will be explicitly recited in the claim, and in the absence ofsuch recitation no such intent is present. For example, as an aid tounderstanding, the following appended claims may contain usage of theintroductory phrases “at least one” and “one or more” to introduce claimrecitations. However, the use of such phrases should not be construed toimply that the introduction of a claim recitation by the indefinitearticles “a” or “an” limits any particular claim containing suchintroduced claim recitation to embodiments containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should be interpreted to mean “at least one”or “one or more”); the same holds true for the use of definite articlesused to introduce claim recitations. In addition, even if a specificnumber of an introduced claim recitation is explicitly recited, thoseskilled in the art will recognize that such recitation should beinterpreted to mean at least the recited number (e.g., the barerecitation of “two recitations,” without other modifiers, means at leasttwo recitations, or two or more recitations).

Furthermore, in those instances where a convention analogous to “atleast one of A, B, and C, etc.” is used, in general such a constructionis intended in the sense one having skill in the art would understandthe convention (e.g., “a system having at least one of A, B, and C”would include but not be limited to systems that have A alone, B alone,C alone, A and B together, A and C together. B and C together, and/or A,B, and C together, etc.). It will be further understood by those withinthe art that virtually any disjunctive word and/or phrase presenting twoor more alternative terms, whether in the description, claims, ordrawings, should be understood to contemplate the possibilities ofincluding one of the terms, either of the terms, or both terms. Forexample, the phrase “A or B” will be understood to include thepossibilities of “A” or “B” or “A and B.”

In addition, where features or aspects of the disclosure are describedin terms of Markush groups, those skilled in the art will recognize thatthe disclosure is also thereby described in terms of any individualmember or subgroup of members of the Markush group. As will beunderstood by one skilled in the art, for any and all purposes, such asin terms of providing a written description, all ranges disclosed hereinalso encompass any and all possible sub-ranges and combinations ofsub-ranges thereof. Any listed range can be easily recognized assufficiently describing and enabling the same range being broken downinto at least equal halves, thirds, quarters, fifths, tenths, etc. As anon-limiting example, each range discussed herein can be readily brokendown into a lower third, middle third and upper third, etc. As will alsobe understood by one skilled in the art all language such as “up to,”“at least,” “greater than,” “less than,” and the like include the numberrecited and refer to ranges which can be subsequently broken down intosub-ranges as discussed above. Finally, as will be understood by oneskilled in the art, a range includes each individual member. Forexample, a group having 1-3 cells refers to groups having 1, 2, or 3cells. Similarly, a group having 1-5 cells refers to groups having 1, 2,3, 4, or 5 cells, and so forth. While various aspects and embodimentshave been disclosed herein, other aspects and embodiments will beapparent to those skilled in the art.

The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopeand spirit being indicated by the following claims.

What is claimed is:
 1. A copper substrate for growing a graphene monolayer, the copper substrate comprising: a first copper layer characterized by a first copper percentage by weight, a first oxygen percentage by weight, and a first average thickness; and a second copper layer in contact with the first copper layer, wherein the second copper layer is characterized by a second copper percentage by weight, a second oxygen percentage by weight, and a second average thickness; wherein: the second copper percentage is greater than the first copper percentage; the second oxygen percentage is about the same or less than the first oxygen percentage; and the second average thickness is less than the first average thickness.
 2. The copper substrate of claim 1, wherein the first average thickness is at least about 3 micrometers.
 3. The copper substrate of claim 1, wherein the second average thickness is one atomic monolayer of copper to about 25 micrometers.
 4. The copper substrate of claim 1, wherein the second copper percentage is greater than the first copper percentage by at least about 0.1%.
 5. The copper substrate of claim 1, wherein: the second copper percentage is at least about 99.9%, the first copper percentage is less than about 99.9%, or the second copper percentage is at least about 99.9% and the first copper percentage is less than about 99.9%.
 6. A system for manufacturing a copper substrate for growing graphene, the system comprising: a deposition chamber; a sample stage configured to hold a copper substrate in the deposition chamber; a copper deposition source; a cleaning agent source configured to direct a cleaning agent to the copper substrate held by the sample stage; a sensor configured to determine a thickness of a layer deposited by the copper deposition source; a heater configured to heat the copper substrate held by the sample stage to an annealing temperature; a gas source configured to provide a thermal annealing gas to the copper substrate held by the sample stage; and a microprocessor coupled to the deposition chamber, the sample stage, the copper deposition source, the cleaning agent source, the sensor, and the beater, wherein the microprocessor is programmable to: employ the cleaning agent source to direct the cleaning agent to a first copper layer of the copper substrate held by the sample stage in the deposition chamber; employ the copper deposition source and the sensor to deposit a second copper layer on the first copper layer, wherein the second copper layer is thinner compared to the first copper layer, and employ the heater and the gas source to thermally anneal the first copper layer at the copper substrate.
 7. The system of claim 6, further comprising: a chemical vapor source that is configured to provide one or more chemical vapor deposition precursors for forming graphene, wherein the microprocessor is further programmable to: employ the chemical vapor source to grow a graphene monolayer at the second copper layer using the one or more chemical vapor deposition precursors for forming the graphene.
 8. The system of claim 7, wherein in a dimension perpendicular to the graphene monolayer, a first copper layer is further characterized by a first average thickness
 9. The system of claim 8, wherein the microprocessor is further programmable to: employ a copper deposition source and a sensor to deposit the second copper layer at a second average thickness that is less than the first average thickness.
 10. The system of claim 6, wherein the annealing temperature is about 800° C. to about 900° C.
 11. The system of claim 6, wherein the second copper layer is saturated in dissolved oxygen at the annealing temperature.
 12. The system of claim 6, wherein the second copper layer is deposited on a surface of the first copper layer by one or more of sputtering, evaporation, electroplating, or chemical vapor deposition (CVD).
 13. The system of claim 6, wherein the microprocessor is further programmable to: employ the heater and the gas source to thermally anneal the first copper layer in an atmosphere comprising: about 1 mole % hydrogen to about 10 mole % hydrogen; and about 90 mole % to about 99 mole % of one or more noble gases.
 14. The system of claim 6, wherein the microprocessor is further programmable to: employ the heater and the gas source to thermally anneal the first copper layer in an atmosphere substantially free of oxygen.
 15. A graphene-copper composite, comprising: a first copper layer characterized by a first copper percentage by weight, a first oxygen percentage by weight, and a first average thickness; a second copper layer having a first surface in contact with the first copper layer, wherein the second copper layer characterized by a second copper percentage by weight, a second oxygen percentage by weight, and a second average thickness; and a graphene monolayer in contact with a second surface of the second copper layer, wherein: the second copper percentage is greater than the first copper percentage; the second oxygen percentage is about the same or less than the first oxygen percentage; and the second average thickness is less than the first average thickness.
 16. The graphene-copper composite of claim 15, wherein the first average thickness is at least about 3 micrometers.
 17. The graphene-copper composite of claim 15, wherein the second average thickness is one atomic monolayer of copper to about 25 micrometers.
 18. The graphene-copper composite of claim 15, wherein the second copper percentage is greater than the first copper percentage by at least about 0.1%.
 19. The graphene-copper composite of claim 15, wherein the first oxygen percentage by weight is about 0.001%.
 20. The graphene-copper composite of claim 15, wherein the second oxygen percentage by weight is about 0.0028%. 